U.S. patent application number 16/343275 was filed with the patent office on 2019-08-22 for ice-based thermal energy storage device.
The applicant listed for this patent is BOREALES ENERGY. Invention is credited to Patrick OUVRY.
Application Number | 20190257593 16/343275 |
Document ID | / |
Family ID | 58054358 |
Filed Date | 2019-08-22 |
United States Patent
Application |
20190257593 |
Kind Code |
A1 |
OUVRY; Patrick |
August 22, 2019 |
ICE-BASED THERMAL ENERGY STORAGE DEVICE
Abstract
Disclosed is a heat exchange device including a first thermally
conductive tube that is hollow over its length, a second thermally
conductive tube that is hollow over its length, and including a
thermally conductive fin, in which the fin extends lengthwise along
the first tube, the fin extends lengthwise along the second tube
and the fin extends width-wise between the first tube and the
second tube.
Inventors: |
OUVRY; Patrick; (Mathieu,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BOREALES ENERGY |
Herouville-Saint-Clair |
|
FR |
|
|
Family ID: |
58054358 |
Appl. No.: |
16/343275 |
Filed: |
October 20, 2017 |
PCT Filed: |
October 20, 2017 |
PCT NO: |
PCT/FR2017/052899 |
371 Date: |
April 18, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28F 1/22 20130101 |
International
Class: |
F28F 1/22 20060101
F28F001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2016 |
FR |
1670616 |
Mar 30, 2017 |
FR |
1752675 |
Claims
1. A heat exchange device, comprising a first thermally conductive
tube (1) that is hollow over a length of said first thermally
conductive tube, a second thermally conductive tube (2) that is
hollow over a length of said second thermally conductive tube, and
a thermally conductive fin (3), in which the fin (3) extends
lengthwise along the first tube (1), the fin (3) extends lengthwise
along the second tube (2) and the fin (3) extends width-wise
between the first tube (1) and the second tube (2).
2. The device according to claim 1, wherein the fin comprises a
first thermally conductive half-fin (6), which extends between the
first tube (1) and a first edge and in which the fin comprises a
second thermally conductive half-fin (7), which extends between the
second tube (2) and a second edge.
3. The device according to claim 1, wherein the thickness of the
fin (3) is less than the width of the first tube (1) and is less
than the width of the second tube (2).
4. The device according to claim 1, wherein the fin (3) is
flat.
5. The device according to claim 1, wherein the first tube (1) is
parallel to the second tube (2).
6. The device according to claim 1, wherein the first tube (1) is
straight over the first tube's length and the second tube (2) is
straight over the second tube's length.
7. The device according to claim 1, wherein the first tube (1) is
made from aluminum, the second tube (2) is made from aluminum and
the fin (3) is made from aluminum.
8. The device according to claim 2, wherein the second half-fin (7)
extends width-wise between the first half-fin (6) and the second
tube (2).
9. The device according to claim 2, wherein the first edge of the
first half-fin (6) is in contact with the second edge of the second
half-fin (7).
10. A method using the device according to claim 1, the method
comprising: evaporating a refrigerant in the first tube (1) and in
the second tube (2), solidifying a liquid material on the first
tube (1), on the second tube (2) and on the fin (3).
11. The method according to claim 10, wherein the liquid material
is water and the refrigerant has an evaporation temperature lower
than the icing temperature of water.
12. A method using the device according to claim 2, the method
comprising: evaporating a refrigerant in the first tube and in the
second tube, solidifying a liquid material on the first tube, on
the second tube and on the fin.
13. A method using the device according to claim 3, the method
comprising: evaporating a refrigerant in the first tube and in the
second tube, solidifying a liquid material on the first tube, on
the second tube and on the fin.
14. A method using the device according to claim 4, the method
comprising: evaporating a refrigerant in the first tube and in the
second tube, solidifying a liquid material on the first tube, on
the second tube and on the fin.
15. A method using the device according to claim 5, the method
comprising: evaporating a refrigerant in the first tube and in the
second tube, solidifying a liquid material on the first tube, on
the second tube and on the fin.
16. A method using the device according to claim 6, the method
comprising: evaporating a refrigerant in the first tube and in the
second tube, solidifying a liquid material on the first tube, on
the second tube and on the fin.
17. A method using the device according to claim 7, the method
comprising: evaporating a refrigerant in the first tube and in the
second tube, solidifying a liquid material on the first tube, on
the second tube and on the fin.
18. A method using the device according to claim 8, the method
comprising: evaporating a refrigerant in the first tube and in the
second tube, solidifying a liquid material on the first tube, on
the second tube and on the fin.
19. A method using the device according to claim 9, the method
comprising: evaporating a refrigerant in the first tube and in the
second tube, solidifying a liquid material on the first tube, on
the second tube and on the fin.
Description
[0001] The invention relates to the technical field of heat
exchangers, and in particular heat accumulators that transfer heat
between a refrigerant and an external phase change or icing-based
material, such as a mixture of water and ice at 0.degree. C., via a
heat-conducting material, such as a metal, separating the
refrigerant and the phase change material. Two significant
parameters for the cost of an exchanger of this type are the volume
of heat-conducting material and the volume of refrigerant used,
with respect to the energy stored.
[0002] Two major families of heat accumulators by phase change are
known from the prior art: [0003] tubular: these accumulators are
made up of a multitude of tubes that are hollow over their length
and parallel to one another, each tube being filled with a
pressurized refrigerant in outer contact with an icing-based
medium. Such tubes are made primarily from a heat-conducting
material, typically metal, in particular steel, aluminum, and more
rarely, copper. [0004] Some tubular accumulators are made up of
plastic tubes. Despite plastic having a thermal resistance greater
than that of metals, their lower cost makes it possible to offset
this handicap by larger exchange surfaces. One variant of these
batteries consists of a single very long tube, arranged in a spiral
or helix or coil. [0005] One variant of these accumulators consists
of circulating a secondary refrigerant in the tubes, typically
glycol water, instead of the refrigerant. [0006] flat: these
accumulators are made up of a multitude of flat exchangers,
parallel to one another. These exchangers are in turn made up of 2
thin flat metal plates, hermetically joined by their edge and spot
welded to one another, arranged at regular intervals with a matrix
distribution (in rows and columns), when the plates are observed on
their largest face. During the manufacture of these exchangers, an
inner space is created by injecting a gaseous or liquid fluid,
under high pressure, until the plates are permanently deformed,
giving the plates a pillow-like appearance, hence their name
"pillow plate". [0007] The inner space of each exchanger is filled
with pressurized refrigerant and the outer surface of each
exchanger is in contact with a medium to be cooled until
icing/ice-formation. [0008] Such pillow plates are made up of
sheets made from a heat-conducting material, typically a metal, in
particular steel (generally stainless) and aluminum. [0009] Some
flat accumulators are made from plastic, again with a thermal
resistance of the plastic greater than that of metals, but at a
lower cost that makes it possible to offset this handicap by
greater exchange surfaces. [0010] One variant of these accumulators
also consists of circulating a secondary refrigerant in the
exchangers, typically glycol water, instead of refrigerant.
[0011] The operation of these phase change heat accumulators,
whether tubular or flat, consists of storing cold as follows:
[0012] producing frigories by evaporating the refrigerant contained
in the inner volume of each exchanger, [0013] initially:
transporting the frigories through the material of the exchanger
into contact with the liquid phase change material, [0014] then
later: transporting the frigories through the material of the
exchanger and the thickness of ice into contact with the
still-liquid phase change material, [0015] solidifying the
still-liquid phase change material that is in contact with the ice
by transferring the frigories from the ice to the material.
[0016] One of the features shared by all of the heat exchangers is
that the evaporation temperature of the refrigerants drops as the
thickness of ice increases. Indeed, the increase of the thickness
of ice over time causes an increase in the thermal resistance,
which opposes the flow of frigories between the refrigerant and the
still-liquid phase change material. To combat this resistance, at a
constant heat exchange power, the refrigerant naturally decreases
its evaporation temperature over time.
[0017] In the prior art, a very different behavior of tubular heat
accumulators is observed relative to flat or plate heat
accumulators, which leads to major differences in terms of energy:
[0018] tubular accumulators: the cold generated within the
exchanger by the evaporation of the refrigerant causes anisotropic
ice formation, i.e., ice growth is concentric to the tubes or
perpendicular to their length or radial with respect to the tubes.
This anisotropic characteristic of the conduction causes a drop in
the evaporation temperature of the refrigerant as a function of
time with a steep slope, of about 2.degree. C./hour. [0019] flat
batteries: the cold generated within the exchanger by the
evaporation of the refrigerant causes ice formation normal or
perpendicular to the two outer surfaces. This characteristic causes
a drop in the evaporation temperature of the refrigerant as a
function of time with a very gentle slope, of about 0.3.degree.
C./h, or about 7 times less than tubular accumulators.
[0020] The study of the behavior of a tubular accumulator and a
flat accumulator, the exchangers of which are manufactured with the
same quantity of thermally conductive material, leads to the
following situation:
[0021] The value "dT", representing the temperature deviation
between the refrigerant, boiling within a thermal accumulator
operating at a constant power, and the phase change temperature of
a phase change material, is equal, after operating for 4 h30, to:
[0022] tubular accumulator: dT=9.4.degree. C. [0023] flat
accumulator: dT=1.4.degree. C.
[0024] Yet it is commonly recognized by the profession that a gain
of 1.degree. C. on the evaporation temperature of a refrigerating
machine corresponds to an increase of its energy efficiency of 2.5
to 3%. In the case at hand, the difference of 8.degree. C.
corresponds to a difference of 20 to 24% in terms of energy
efficiency.
[0025] But this strong improvement in the energy efficiency has a
cost: flat batteries are more expensive to produce (very long
welding lengths) and require a significant volume of
refrigerant.
[0026] There is therefore an unmet need in the prior art for a
device for a heat exchanger, imparting a thermodynamic performance
close to that of flat exchangers, using a volume of refrigerant
close to or less than that of tube exchangers, with an identical
volume of thermally conductive material, and the welding lengths of
which are close to or less than those of tube exchangers.
[0027] Furthermore, tubes with fins or radiators are known in the
prior art, for discharging, by fins, the heat produced by tubes
filled with a heat transfer fluid and bathing in air, by convection
in air. However, the fins of these tubes are used in the prior art
to move the heat away from a tube as much as possible. From there,
the fins are not considered suitable for use with matrixes of
tubes, which are necessarily as close as possible in a heat
accumulator. Indeed, the heat moved away by the fins is presumed to
be communicated to the adjacent fins and tubes, which then
decreases the efficiency of the assembly and its radiator
function.
[0028] In general, in the prior art, an unfavorable prejudice
exists against the use of fins in a heat accumulator, including
against ice formation, the heat function of the fins for moving the
heat away from the tubes being incompatible with the closeness of
the tubes necessary in a heat accumulator to maximize icing in a
given enclosure volume of the heat accumulator.
[0029] In this context, the invention is a heat exchange device,
characterized in that it comprises a first thermally conductive
tube that is hollow over its length, a second thermally conductive
tube that is hollow over its length, and a thermally conductive
fin, in which the fin extends lengthwise along the first tube, the
fin extends lengthwise along the second tube and the fin extends
width-wise between the first tube and the second tube.
[0030] In variants of the device:
[0031] the fin comprises a first thermally conductive half-fin,
which extends between the first tube and a first edge and in which
the fin comprises a second thermally conductive half-fin, which
extends between the second tube and a second edge.
[0032] the thickness of the fin is less than the width of the first
tube and is less than the width of the second tube.
[0033] the fin is flat.
[0034] the first tube is parallel to the second tube.
[0035] the first tube is straight over its length and the second
tube is straight over its length.
[0036] the first tube is made from aluminum, the second tube is
made from aluminum and the fin is made from aluminum.
[0037] the second half-fin extends width-wise between the first
half-fin and the second tube.
[0038] the first edge of the first half-fin is in contact with the
second edge of the second half-fin.
[0039] The invention also relates to a method using the device as
defined above, characterized in that it comprises the following
steps:
[0040] evaporating a refrigerant in the first tube and in the
second tube,
[0041] solidifying a liquid material on the first tube, on the
second tube and on the fin.
[0042] In a variant of the method, the liquid material is a water
and the refrigerant has an evaporation temperature lower than the
icing temperature of water.
[0043] The various embodiments of the invention are described for
the references to numbers in parentheses, in connection to a list
of figures provided with the present application, in which:
[0044] FIG. 1 shows a device according to the invention with a
continuous fin joining two hollow tubes.
[0045] FIG. 2 shows a device according to the invention with a
discontinuous fin between the two hollow tubes, made up of two
half-fins extending between the tubes.
[0046] Different embodiments of the invention are described
below.
[0047] In a first embodiment, the heat accumulator is made up of
tubes arranged in parallel in a plane. A flat fin that is thin
compared to the width of the tubes, which is their diameter for
cylindrical tubes of revolution, is arranged between the tubes in
the plane of the tubes. The tubes and the fin are arranged in a
shell containing water at atmospheric pressure. A refrigerant,
which is for example a refrigerant of type R134a, the evaporation
temperature of which is below the freezing temperature of water, or
273.degree. Kelvin, in a given pressure range, is circulated by a
refrigeration machine comprising a compressor, able to operate in
this pressure range.
[0048] FIG. 1 thus shows a characterizing part of the heat
accumulator above in which a first tube (1) and a second tube (2)
are connected along their length by a continuous flat fin (3) that
extends over the entire width between the first tube (1) and the
second tube (2).
[0049] The first tube (1), the second tube (2) and the fin (3) are
for example made from aluminum or a thermally conductive material
and make it possible to obtain, by extrusion, a homogeneous part
integrally molded in one piece including the first tube (1), the
second tube (2) and the fin (3) in a continuous assembly.
[0050] Preferably, the first tube (1) and the second tube (2) have
the same length, the same width and the same thickness and are
cylindrical and of revolution around a first axis for the first
tube (1) and a second axis for the second tube (2).
[0051] The fin preferably has a minimal thickness allowed by the
extrusion method, i.e., between 1 mm and 1.5 mm, but it also has a
thickness smaller than the width or diameter of the tubes and
preferably about the thickness of the tubes, here 1.5 mm. It also
has a width equal to the distance between the tubes and this
distance between the tubes is chosen to be greater than ten times
the width of a tube. For example, a width of the tubes of 8 mm and
a thickness of the tubes of 1.5 mm can be chosen, and a distance
between the axes of the tubes of 100 mm, giving a fin width of 92
mm.
[0052] In all cases, a criterion of the invention can be verified
for any geometry of tubes and fin. This criterion can be obtained
experimentally by introducing the device according to the invention
into a heat accumulator and tracing, as a function of time at a
constant refrigeration power, the drift of the evaporation
temperature of the refrigerant in the accumulator, or "dT" as
previously indicated. For example, a pressure gauge can be used
conventionally and the temperature of the fluid, such as the R134a,
can be deduced by the curve of the saturated vapor pressure as a
function of the temperature of the mixture.
[0053] For a system according to the invention, one can see that
the curve representing the "dT" as a function of time has a slope
very close to that of flat exchangers, and therefore very different
from the slope of tube exchangers.
[0054] The system according to the invention therefore does not
work like a tube system, but like a plate system in terms of icing.
One can therefore deduce that the system according to the invention
allows anisotropic icing, like flat exchangers, while making it
possible to use a much smaller volume of refrigerant than that of a
tube system, and a fortiori the volume of refrigerant of a flat
system.
[0055] Several variants of the system of FIG. 1 can be considered,
in particular the fin can have a different shape from a plane,
outside the plane of the axes of the tubes, the tubes can be not
strictly parallel and can be straight or rectilinear or curved with
different shapes over their length, with a circular or elliptical
or even rectangular section.
[0056] The material of the tubes and the fin can be a thermally
conductive material, other than aluminum, such as a metal, in
particular stainless steel or copper.
[0057] The variants will be favored that use the least amount of
material and the least amount of refrigerant, while continuing to
operate as a plate system, in terms of the evaporation temperature
drift over the course of icing.
[0058] The fin thermally connecting the tubes changes its behavior
during icing and makes it possible to place a small number of tubes
to thermally re-create the operation of a plate.
[0059] Furthermore, practically, the first tube (1) has,
diametrically opposite the fin (3) in the plane of the tubes, a
third half-fin (4), with the same thickness as the fin (3) and a
width for example equal to half the width of the fin (3).
[0060] Likewise, the second tube (2) has, diametrically opposite
the fin (3) in the plane of the tubes, a fourth half-fin (5), with
the same thickness as the fin (3) and a width for example equal to
half the width of the fin (3).
[0061] In a second embodiment of the invention, which is also the
preferred embodiment for the invention, the fin is made
discontinuously between the first tube (1) and the second tube (2)
in the form of a fin cut into two half-fins along its length: a
first half-fin (6) starting from the first tube (1) up to a first
edge and a second half-fin (7) starting from the tube (2) up to a
second edge.
[0062] The cutting of the fin into two half-fins can be done along
an edge with any shape without going beyond the teaching of the
present application. However, a straight shape of the edges is
particularly advantageous. Indeed, the structure of the invention
in this second embodiment can be made from a single extruded piece
comprising a central tube and two lateral half-fins in a same
plane. It is thus possible to make the device illustrated in FIG. 2
by taking two of these parts extruded parts and making their tubes
parallel and their fins coplanar in the plane of the tubes.
[0063] When the facing edges of two half-fins mechanically touch,
one thus obtains the thermal equivalent of an extruded part with a
width equal to that of a part multiplied by the number of parts
used.
[0064] When the facing edges are separated, one obtains icing
between the edges and a practically unchanged operation relative to
the joint plates.
[0065] Outside a transitional state for the first embodiment and
the second embodiment, the flow of frigories in the middle of the
fin (3) is nil and the flow of frigories between the first half-fin
(6) and the second half-fin (7) is nil.
[0066] By comparison with the existing accumulators, one can see
the following features of the second embodiment for joined facing
edges.
TABLE-US-00001 Battery Second Type Tubular Flat embodiment Units
"dT" at 4h30 9.4 1.4 2.9 .degree. C. Length of welds 5 10 1 meter
Quantity of fluid 2 4 0.4 liter Pressure holding 50 10 50 Bar
[0067] Synthetically, it emerges that the battery according to the
second described embodiment is the least expensive of the three to
manufacture (5 to 10 times less welding), that it is also the least
expensive to use (energetically conservative and requires 5 to 10
times less refrigerant than the other two techniques), for
resistance to pressure equal to or greater than the other two.
[0068] To obtain this comparative table, the modeling and
simulation hypotheses are as follows: [0069] equivalent thermal
power for all three types of battery. [0070] identical quantities
of thermally conductive material for the heat for all three types
of accumulator.
[0071] One skilled in the art may, by a simple operations or by
applying the "dT" criterion proposed in the first embodiment and in
the second embodiment, verify, for a structure of these first and
second embodiments, whether the behavior of the selected geometric
structure is indeed a thermal behavior similar to a pillow plate or
plate.
[0072] In particular, for a structure operating according to the
invention, the curve of the evolution of "dT" as a function of time
or over time, will have a slope very close to the same curve drawn
for a flat exchanger, with a practically constant shift. This shift
will be about 1.5.degree. C. after 4 h30.
[0073] In the device of FIG. 2, the third half-fin (4) is
diametrically opposite the first half-fin (6) on the first tube (1)
and the fourth half-fin (5) is diametrically opposite the second
half-fin (7) on the second tube (2). One can indeed see in this way
that this embodiment can be obtained by arranging, mechanically
fixed in the same plane, two identical extruded parts, one made up
of the first tube (1), the first half-fin (6) and the third
half-fin (4) and the other of the second tube (2), the second
half-fin (7) and the fourth half-fin (5).
[0074] For example, the tubes have an outer diameter of 8 mm and an
inner diameter of 5 mm for a thickness of 1.5 mm. Each half-fin has
a width of 46 mm, for a width of about 100 mm of each extruded part
and a thickness of the half-fins of 1.5 mm. The edges of facing
half-fins are preferably joined. Like for the first embodiment, the
distance between the tubes, here twice 46 mm for joined fins, is
chosen to be greater than ten times the width of a tube, here 8
mm.
[0075] The same variants as in the first embodiment can be
considered on the shape of the tubes and half-fins and their
component material, which is typically a metal suitable for
extrusion.
[0076] Furthermore, in this embodiment, it is desirable to place
the facing edges of the half-fins in mechanical contact, to
maximize the storage energy density of the accumulator.
[0077] For this embodiment, it is possible to consider half-fins
with different widths.
[0078] Typically in the described embodiments, the ratio of the
inner surfaces, presumed to be smooth, in contact with the
refrigerant and the outer surfaces in contact with the phase change
material is greater than 10. This constitutes an unusual anisotropy
in the prior art for a tube with lateral fins. However, despite
such an anisotropic ratio, thermal simulations using methods known
from the prior art show that 3 times more heat is exchanged via the
fin or the half-fins than via the tube, which indeed validates the
influence of the fin on the icing.
[0079] For all of the described embodiments, it will be possible to
use tube or fin or half-fin structures in a refrigeration machine
as evaporator, to cool and solidify, using a refrigerant
evaporating in the tubes, a liquid material, preferably calm or
immobile, surrounding the tubes and the fins or half-fins.
[0080] The invention is open to industrial application or useful in
the field of heat accumulators, transferring heat between two phase
change materials and in particular for storing energy in the form
of ice from freshwater or saltwater or brackish water.
[0081] Throughout the application, the addition of a "frigorie" to
a thermodynamic system will be defined as the removal of a calorie
from that thermodynamic system.
* * * * *